The lack of a functioning radio communications system within the London Underground limited the response to the 7 July bombings last year, a new report has concluded.

Emergency workers were forced to run back and forth between trains, platforms and the surface to communicate since no mobile radio communications systems were available in the tube.

The four bombs, detonated on a bus and at three Underground locations, killed 56 people and injured more than 700.

Near one of the bombing sites, Russell Square station, a 'leaky feeder' two-way antenna system used by train drivers to communicate with their line control managers was damaged in the explosion.

Mobile phones do not work in the tunnels. Work on the ageing train system is difficult because of the narrowness of the tunnels.

The authority responsible for the Underground, Transport for London, is investing £2bn to install a digital radio system in the tunnels, some of which date back to the mid-1800s. The plan spans 20 years.

But the report, produced by the 7 July Review Committee, said the time scale is too long, and an interim system should be identified. "Digital radio will be crucial in the event of a future emergency on the tube," it said.

By the end of 2007, London's police, fire and ambulance authorities are scheduled to complete rolling out an interoperable digital radio system, under the names Airwave and Connect. That system will also work in underground tunnels.

While responding to the bombings, the city's emergency service relied too heavily on mobile phones, leading to communications problems on jammed networks.